The present invention relates to a method and apparatus for preventing the formation of leachable mercury in mercury arc vapor discharge lamps. More particularly, the present invention relates to a method and apparatus for preventing the formation of leachable mercury that involves coating metallic components in mercury arc vapor discharge lamps with at least one noble metal coating.
Mercury arc vapor discharge lamps, otherwise commonly known as fluorescent lamps, are standard lighting means. The mercury arc vapor discharge lamp consists of metallic components such as lead wires, connector pins and end caps. The lead wires and portions of the end cap and connector pins are surrounded by a glass enclosure. The interior of the glass enclosure is typically coated with phosphor. Elemental mercury is added to the mercury arc vapor discharge lamp and typically, the elemental mercury adheres to the phosphor. In certain conditions, it has been found that when elemental mercury comes in contact with the metal components in a lamp such as copper and iron containing lead wires, brass pins, or other associated metallic mount components, the elemental mercury is transformed into a leachable form.
In order to address the growing concern that mercury from disposal of fluorescent lamps might leach into surface and subsurface water, the Environmental Protection Agency has established a maximum concentration level for mercury at 0.2 milligrams of leachable mercury per liter of extract fluid. The concentration level for mercury is generally determined by a standard analysis known as the Toxicity Characteristic Leaching Procedure (TCLP), a well known test procedure.
When carrying out the TCLP test, test lamps are pulverized to form lamp waste material similar to that which would result from lamp disposal in land fills or other disposal locations. The ambient conditions in disposal locations may be such as to promote formation of leachable mercury. The TCLP test conditions themselves tend to allow for formation of leachable mercury in amounts greater than the established limit of 0.2 milligrams per liter.
During the disposal of the lamp, and in the TCLP test, the glass enclosure of the lamp is broken. Elemental mercury that is contained in the lamp is then exposed to the metal components in an aqueous environment. Elemental mercury, when exposed to both the metal components and the aqueous environment, is oxidized to leachable mercury. The metal components in the lamp provide the source of oxidizable iron and oxidizable copper which promotes the formation of leachable mercury.
Several techniques have been developed which prevent the formation of mercury which can leach into the environment. The methods currently used are concerned with a method of delivering a chemical agent or metal upon disposal of a lamp or during the TCLP test. For instance, Fowler et al. (U.S. Pat. No. 5,229,686 and U.S. Pat. No. 5,229,687) describe methods which incorporate chemical agents in the lamp in either a glass capsule or the basing cement. These chemical agents include various salts such as bromide anions, chloride anions, iodide anions, iodate anions, periodate anions, and sulfide anions, to name a few. Other chemical agents include powders such as iron powder, copper powder, tin powder, and titanium powder.
Generally, any modification of the lamp components are driven by the need to decrease the amount of leachable mercury. Unfortunately, the current methods are concerned with a method of delivery to add significant amounts of a chemical or a metal in the lamp. In addition, the method of delivery of the chemical agents typically modify the lamp design. Thus, methods have yet to be devised which improve the existing components to decrease the amount of leachable mercury.
The invention provides a method and articles made thereby for preventing the formation of leachable mercury in mercury vapor discharge lamps. The method includes coating at least one of the metallic components in the mercury vapor discharge lamp with at least one noble metal coating.